The present invention generally relates to multi-energy imaging acquisitions. While it is described with particular application to medical imaging, in particular computed tomography (CT), it also relates to other applications in which it is desirable to reconstruct images from scans of photons with different energies.
In CT a radiation source, present in a gantry that is rotatable around an examination area, emits photons, usually x-rays. A detector, generally opposite the radiation source, detects the photons after they traversed the examination area, usually to scan a body present in said examination area. In multi-energy CT the radiation source emits photons at two (or more) different energy levels, which are attenuated at different levels by different materials in the object, e.g. various organs, fluids or bones within a patient's body. Multi-energy CT is used to increase inherently weak soft-tissue contrasts in x-ray imaging and at the same time allows for reduction of beam-hardening artifacts. Among various multi-energy CT techniques (including dual source CT and use of multi-layer detectors or photon-counting detectors), a peak kilovoltage (kVp) switching technique is of particular interest, since it operates with a conventional detector.
The kVp-switching technique is based on acquisition of projections at two (or more) different anode voltages, i.e. different photon spectra. An example of kVp-switched CT may be found in U.S. patent application Ser. No. 2011/0085719A1, wherein a set of first (low kVp) image scans and a set of second image scans (high kVp) are acquired interleaved as a function of a rotation angle of the gantry. An image is reconstructed from the obtained first and second image scans.
When demanding a constant x-ray dose and scan time, angular undersampling occurs with interleaved projection sets, since these consist of fewer projections than a conventional ‘complete’ CT acquisition. This angular undersampling often leads to artifacts, such as streak artifacts and moiré patterns, in reconstructed images. The present invention aims at mitigating such undersampling artifacts resulting from interleaved multi-energy imaging acquisitions.